Field of the Disclosure
The present subject matter relates to devices and methods for measuring and/or adjusting the spacing between two opposing surfaces, such as adjacent vertebral bodies.
Description of Related Art
The spacing in the disc space between adjacent vertebral bodies may decrease for any of a number of reasons, including traumatic impacts and degenerative diseases. Improper spacing between adjacent vertebral bodies can lead to varying degrees of discomfort and/or pain and, if severe enough, may be reason for surgical correction of the spacing. One known method for surgical disc space sizing involves using traditional manual spreaders, which are often in the form shown in FIG. 1. Such known disc spreaders S are generally paddle-shaped, with one cross-sectional dimension H (referred to herein as its height) that is greater than another cross-sectional dimension W (referred to herein as its width). The distal end of the spreader S is inserted into the disc space in a flat orientation (i.e., with the plane of the spreader height H oriented parallel to the endplates of adjacent vertebral bodies) and then it is rotated 90° to re-orient the plane of the spreader height H perpendicular to the endplates. The height H of the spreader S is selected to equate to the proper separation between the adjacent vertebral bodies, such that the edges of the re-oriented spreader S contact the endplates and force proper spacing within the disc space. To accommodate different spacing situations, a set of spreaders is typically provided with a variety of heights H, which may range from 8 mm to 14 mm in 1 mm increments.
One disadvantage to such an approach is that the means for delivering the distal end of the spreader S to the disc area (e.g., a working cannula) must be large enough to accommodate the height H. Accordingly, a relatively large delivery cannula or means is required to accommodate the larger-sized spreaders. Larger spreaders also require a larger access site, resulting in greater surgical resection and more retraction of nerve roots and other surrounding structures. This can lead to the possibility of greater trauma, loss of blood, and pain, as well as potentially increased surgical and recovery time. Another disadvantage is that each spreader is appropriate for only one separation amount, so if a particular spreader is initially used and found to result in improper spacing, it must be removed and the process repeated with a spreader having a different width. The multiple tool exchanges inherent in such an iterative sizing procedure increases the risk of damaging nerve roots or other surrounding structures. Yet another possible disadvantage of the spreader S of FIG. 1 is that, as it is rotated between the endplates to achieve full height, the pressure applied by the rotating edge and, ultimately, the final edge of the spreader S are known to cause gouging and damage to the endplates. This damage can interfere with the fusion process and the placement of interbody devices into the disc space to facilitate fusion. Accordingly, it would be advantageous to provide a sizing device with contact surfaces that do not rotate into contact with the endplates, but instead are brought into contact therewith over a larger surface area.
Additional known spreaders are described in PCT publication no. WO/2011/150350, which is hereby incorporated herein by reference. The devices and methods described in PCT publication no. WO/2011/150350 represent an improvement to spreaders of the type illustrated in FIG. 1, but there remains room for improvement of the means and method for delivering and deploying such spreaders in the disc space.